Target is offering a 10 percent discount this weekend after a data security breach this week exposed 40 million shoppers to credit and debit card fraud.

A security expert who revealed the data breach says the cards are flooding the black market. The stolen accounts are being sold in batches of one million. Some are selling for as much as $100 per card.

In addition to credit card numbers, the data stolen includes names, expiration dates and the three-digit security codes. Internet sales were not affected, only cards used in-store.

The first class action suit against the company was filed Thursday in San Francisco Federal Court.

Target says the hack has been fix, but many customers aren’t convinced. Shoppers at the retail chain used mostly cash on Friday.

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"It's just one of those things that you have to do to take care of yourself," customer Tom Eversole told ABC News.

This particular privacy breach appears to be different from the usual hacking into company servers and “may have involved tampering with the machines customers use to swipe their cards when making purchases,” according to the Wall Street Journal.

A similar security breach at T.J. Maxx in 2007 left 90 million shoppers exposed to fraud.